The invention relates to thermoplastic compositions and more particularly to polycarbonate compositions having high impact strength at low temperatures.
A thermoplastic molding composition suitable for making articles having good combination of properties is disclosed. The composition contains 80 to 60 percent of (A) a copolycarbonate wherein 65 to 75 mole percent of its structural units are derived from compounds of formula (I) 
wherein R1 to R4 independently of one another represent H, C1-C4-alkyl, phenyl, substituted phenyl or halogen, and wherein 25 to 35 mole percent of its structural units are derived from compounds of formula (II) 
wherein R5 to R8 independently of the others denote H, CH3, Cl or Br and X is C1-C5-alkylene, C2-C5-alkylidene, C5-C6-cycloalkylene, C5-C10-cycloalkylidene, and 20 to 40 percent of (B) a homopolycarbonate of bisphenol A having a melt flow rate, determined in accordance with ASTM D-1238 under 1.2 kg loading, at 300xc2x0 C. of 3 to 12 gm/10 minutes, the percents in both occurrences being relative to the weight of the composition.
Need has long been indicated for transparent, thermally stable polycarbonates that, in comparison to conventional Bisphenol-A based homopolycarbonates, also feature improved resistance to chemicals and better impact strength at low temperatures.
Copolycarbonates based on 4,4xe2x80x2-dihydroxydiphenyl (herein xe2x80x9cDODxe2x80x9d) and 2,2-bis(4-hydroxyphenyl)propane are already known from JP5117382, EP 544 407 and U.S. Pat. Nos. 5,470,938; 5,532,324 and 5,401,826 These are disclosed as being resistant to chemicals and heat and are flame retardant, while having the same mechanical properties and transparency as commercially available homopolycarbonate of bisphenol A.
DE 10047483.7 describes copolycarbonates of 4,4xe2x80x2-dihydroxydiphenyl and 2,2-bis(4-hydroxyphenyl)propane (bisphenol A) that exhibit particularly good low-temperature properties. However, it is also described that the good low-temperature properties diminish as the content of 4,4xe2x80x2-dihydroxydiphenyl falls. Since 4,4xe2x80x2-dihydroxydiphenyl is an expensive component in comparison with 2,2-bis(4-hydroxyphenyl)-propane, it is desirable for reasons of cost to keep the 4,4xe2x80x2-dihydroxy-diphenyl content as low as possible, without losing the desired improvement in the low-temperature strength.
A presently pending patent application Ser. No. 10/196,874 disclosed blends containing copolycarbonates of DOD and homopolycarbonate of bisphenol A that exhibit highly desirable properties.
There is a need in material suitable for applications where low temperature impact strength is required. The impact strength is that which is determined as notched Izod and as multiaxial impact strength. It has now been found that the art has not recognized the critical dependence of the multi-axial impact strength at low temperatures on the melt flow rate of the homopolycarbonate component. It has also been found that not all the blends thus disclosed are the equivalents to one another and that compositions within a narrowly defined range exhibit surprising and unexpected properties.
Accordingly, the present invention relates to a thermoplastic molding composition containing 80 to 60, preferably 65 to 75, percent of (A) a copolycarbonate wherein 65 to 75, preferably 68 to 73, mole percent of its structural units are derived from compounds of formula (I) 
wherein R1, R2, R3 and R4 independently of one another represents H, C1-C4-alkyl, phenyl, substituted phenyl or halogen, preferably H, C1-C4-alkyl or halogen, and particularly preferably all represent the same radical, especially H or tert-butyl, and 25 to 35, preferably 27 to 32, mole percent of its structural units are derived from compounds of formula (II) 
wherein R5, R6, R7 and R8 independently one of the others denote H, CH3, Cl or Br and X is C1-C5-alkylene, C2-C5-alkylidene, C5-C6-cycloalkylene, C5-C10-cycloalkylidene, and
20 to 40, preferably 25 to 35, percent of (B) a homopolycarbonate of bisphenol A, having a melt flow rate, determined in accordance with ASTM D-1238 under 1.2 kg loading, at 300xc2x0 C. (herein xe2x80x9cMFRxe2x80x9d) of 3 to 12 gm/10 minutes, the percents, both occurrences being relative to the weight of the composition.
Surprisingly, it has now been found that the polycarbonate blends according to the invention have good low-temperature properties including notched Izod and multi-axial impact strength.
The inventive composition is useful in making molded articles wherever the properties profile of conventional polycarbonate and copolycarbonate is insufficient. Particular applicability of the composition is indicated in the electrical and construction sectors, including glazing, especially in the automotive sector as well as in making films, sheets, fittings or housing parts where dimensional stability under heat, chemical resistance and good low-temperature properties are required.
According to the invention, low temperatures are to be understood as being temperatures below 0xc2x0 C., particularly preferably below xe2x88x9210xc2x0 C., most particularly preferably below xe2x88x9230xc2x0 C.
Suitable compounds of formula (I) include 4,4xe2x80x2-dihydroxydiphenyl (DOD) and 4,4xe2x80x2-dihydroxy-3,3xe2x80x2,5,5xe2x80x2-tetra(tert-butyl)diphenyl, 4,4xe2x80x2-dihydroxy-3,3xe2x80x2,5,5xe2x80x2-tetra(n-butyl)diphenyl and 4,4xe2x80x2-dihydroxy-3,3xe2x80x2,5,5xe2x80x2-tetra(methyl)diphenyl. 4,4xe2x80x2-dihydroxydiphenyl is particularly preferred.
Suitable compounds of formula (II) are 2,2-bis(4-hydroxyphenyl)propane, 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane and 1,3-bis[2-(4-hydroxyphenyl)-2-propyl]benzene, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, 1,1-bis(4-hydroxyphenyl)-cyclohexane, especially 2,2-bis(4-hydroxyphenyl)propane (bisphenol A) and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (bisphenol TMC). Particularly preferred is 2,2-bis(4-hydroxyphenyl)propane (bisphenol A).
The copolycarbonate (A) may be derived from one or more compounds of formula (I) and one or more compounds of formula (II).
The preparation of (co)polycarbonates is known.
The preparation of polycarbonates by the interfacial process or by the melt transesterification process is known. Reference is made in this connection to xe2x80x9cSchnellxe2x80x9d, Chemistry and Physics of Polycarbonates, Polymer Reviews, Vol. 9, Interscience Publishers, New York, London, Sydney, 1964, p. 33 ff and to Polymer Reviews, Volume 10, xe2x80x9cCondensation Polymers by Interfacial and Solution Methodsxe2x80x9d, Paul W. Morgan, Interscience Publishers, New York 1965, Chap. VIII, p. 325, incorporated herein by reference.
Generally, the preparation of copolycarbonates involving compounds of formula (I) takes place preferably in solution, namely by the interfacial process or the process in homogeneous phase. Preparation by the melt transesterification process is also possible, which process is described, for example, in DE-A 19 64 6401 or in DE-A 1 42 38 123. Transesterification processes are also described in U.S. Pat. Nos. 3,494,885; 4,386,186; 4,661,580; 4,680,371 and 4,680,372 (all incorporated by reference herein) and in EP 26120, 26121, 26684, 28030, 39845, 91602, 97970, 79075, 146887, 156103, 234913, 240301 and in DE1495626 and 2232977.
The polycarbonate and copolycarbonate according to the invention preferably contain structural units derived from any of a variety of chain terminators. Suitable chain terminators include ones conforming to formula (III) 
wherein R, Rxe2x80x2 and Rxe2x80x3 each independently of the others represent H, optionally branched C1-C34-alkyl or cycloalkyl, C7-C34-alkaryl or C6-C34-aryl. The preferred chain terminators include butylphenol, tritylphenol, cumylphenol, phenol and octylphenol. The most preferred are butylphenol and phenol. The chain terminators used in the making of copolycarbonate (A) may be either the same as or are different from the ones used in the preparation of polycarbonate (B).
The individual components (A) and (B) may, independently of each other, contain small amounts of from 0.02 to 3.6 mol % (based on the dihydroxy compound) of branching agents. Suitable branching agents are compounds having three or more functional groups, preferably those having three or more phenolic OH groups, for example, 1,1,1-tri-(4-hydroxyphenyl)ethane and isatin biscresol.
In order to alter the properties of the inventive compositions, additives, fillers and/or reinforcing agents may be incorporated. These include thermal stabilizers, UV stabilizers, flow modifiers, mold-release agents, flame retardants, pigments, finely divided minerals, fibrous substances, flame retardant agents, such as alkyl and aryl phosphites, phosphates, phosphanes, low molecular weight carboxylic acid esters, halogenated compounds, salts, chalk, quartz powder, glass fibers and carbon fibers, pigments and combinations thereof. Such compounds that are known in the art for their efficacy in imparting special effects or properties to thermoplastic polycarbonate compositions are known and have been disclosed in xe2x80x9cPlastics Additivesxe2x80x9d, R. Gxc3xa4chter and H. Mxc3xcller, Hanser Publishers, 1983, incorporated herein by reference.
Other polymers, for example polyolefins, polyurethanes, polyesters, acrylonitrile-butadiene-styrene and polystyrene, may also be blended with the components of the inventive composition.
Such substances may be added to the inventive composition by conventional means and following conventional procedures.
The components (A) and (B) have weight-average molecular weights of 10,000 to 60,000, preferably 20,000 to 55,000, as determined at room temperature by relative solution viscosity (solution of 0.5% by weight) in dichloromethane or in mixtures of equal amounts by weight of phenol/o-dichlorobenzene, calibrated by light scattering.
The polycarbonate blends according to the invention are thermoplastically processable conventionally at temperatures of 240xc2x0 C. to 380xc2x0 C., preferably 260xc2x0 C. to 360xc2x0 C. Molded articles and films of any kind may be produced in a known manner by means of injection molding or by extrusion. The present application relates also to molded articles and extrudates produced from the inventive composition.
The inventive composition is readily soluble in solvents such as chlorinated hydrocarbons, for example, methylene chloride, and may thus be processed, for example, in a known manner to cast films.